(1) Field of the Invention
The present invention relates to a method for producing a 5-bromo-1-pentanal compound or an acetal derivative thereof.
More particularly, the present invention relates to a method for producing a 5-bromo-1-pentanal compound or an acetal derivative thereof from a corresponding 4-pentenal compound or an acetal derivative thereof, without decomposing or modifying the formyl or formyl acetal radical in the pentenal compound.
The 5-bromo-1-pentanal compound or the acetal derivative thereof has a backbone chain having five carbon atoms, a terminal of the chain consisting of a bromine atom and an opposite terminal of the chain consisting of an aldehyde or acetal, and thus is a bi-functional compound. Therefore, this compound is very useful as a molecular backbone chain-forming element when a physiologically active compound, for example, an indole alkaloid or a tri-cyclic sesquiterpen, is synthesized.
(2) Description of the Related Arts
It is known that a 5-bromo-1-pentanal compound can be produced by the following conventional methods.
(A) M. Akhtar et al., J. Am. Chem. Soc., 87, 1807 (1965) discloses a method of producing a 5-bromo-1-pentanal compound by the ring cleavage and bromination reaction of a cyclopentanol compound.
(B) J. F. Le Borgne, J. Organomet, Chem., 122, 123 (1976) discloses a method of producing a 5-bromo-1-pentanal compound by the alkylation of a corresponding aldimine compound with a dibromo-alkane.
(C) W. Oppolzer et al., Helv. Chem. Acta., 60, 1801 (1977) discloses a hydroboration of a 2-substituted-4-pentenal compound to produce a 5-bromo-1-pentanal compound.
(D) R. Daniel Little et al., J. Org. Chem., 47, 362 (1982) discloses a process for producing a 5-bromo-1-pentanal compound by partially reducing a corresponding 5-bromovaleronitrile and by hydrolyzing the partially reduced compound.
(E) M. E. Kuehne et al., J. Org. Chem., 43 3705 (1978) discloses a production of a 5-bromo-1-pentanal compound by reducing a corresponding 5,5-dimethoxyvaleric acid methylate, by converting the reduced product to the mesityl derivative thereof and then substituting the mesityl derivative with a bromine atom.
The above-mentioned methods (A) and (B) are disadvantageous in that the yield of the aimed compound is unsatisfactorily low, and thus is not suitable for industrial use.
The above-mentioned methods (C), (D), and (E) are disadvantageous in that an expensive compound such as diborane, butylaluminum hydride or lithium bromide must be used, and when the above-mentioned compound is used in a large amount, performance of these methods becomes increasingly dangerous, and thus they are not always usable for industrial purposes.
Generally, it is known that an aliphatic compound having a molecular terminal thereof consisting of a bromine atom can be produced by the anti-Markownikoff reaction of a corresponding aliphatic compound having a molecular terminal thereof consisting of a CH.sub.2 .dbd.CH-bond. However, the anti-Markownikoff reaction between an aliphatic compound having a molecular terminal thereof consisting of a CH.sub.2 .dbd.CH-bond and an opposite molecular terminal thereof consisting of a formyl radical (--CHO) and hydrogen bromide was not known before the present invention.
When the anti-Markownikoff reaction is applied to an aliphatic compound having the molecular terminal thereof consisting of a CH.sub.2 .dbd.CH-bond and the opposite terminal thereof consisting of a formyl radical, under usual reaction conditions, it was believed that the formyl radicals will release proton therefrom and be easily converted to carbonyl radicals. The resultant proton serves as a chain transfer agent and will cause undesirable other side-reactions to occur, and these side-reactions will result in a low yield of the aimed 5-bromo-1-pentanal compound or acetal derivative thereof.
Under the above-mentioned circumstance, there is a strong demand for a new method which can produce a 5-bromo-1-pentanal compound or the acetal derivative thereof at a high yield.